It is known that such depollution means can include, for example, a NOx trap which is a system for reducing polluting emissions from motor vehicle engines.
The engine is then associated with means for controlling its operation to switch said operation between a standard lean mode of operation and a nominal rich mode of operation for regeneration, depending on various engine operation control parameters.
In the standard lean mode of operation, the NOx trap stores NOx, and once the trap has become saturated, regeneration thereof is triggered by switching the engine to operate in its rich mode of operation in order to destock the NOx, in which mode the engine produces reducing agents such as CO and HC, for example.
In conventional manner, this is performed by modifying at least one engine operation control parameter, i.e. at least one parameter relating to the injection of fuel into the engine (quantity, timing phase, pressure, etc. . . . ) and/or at least one parameter of the engine air feed loop (air flow rate, recycling, turbocompressor pressure, etc. . . . ).
In particular, during this operation of the engine in its nominal rich mode for regeneration, use is made of post-injection of fuel into the cylinders of the engine. Likewise, the engine is operated with post-injection for the purpose of regenerating a particle filter included in the exhaust system.
Post-injection is injection of fuel after top dead center (TDC).
Unfortunately, such post-injection leads to the engine lubricating oil being diluted by the fuel that is post-injected into the engine.
Oil becomes diluted because post-injection takes place late in the engine cycle and a large fraction of the fuel is then injected against the walls of the combustion chamber.
A tiny fraction of the fuel then passes into the sump via the piston ring.
Consequently the lubricating oil becomes diluted with fuel.
Such dilution of the oil can lead to a loss of oil viscosity and thus of oil pressure, giving rise to premature aging or indeed dilution of additives present in the oil.